Siemens LOGO!, Manual

Page: 153 / 534

LOGO! functions
4.3 Special Functions
LOGO!
Manual, 04/2011, A5E03556174-01
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4.3.4 Retentivity
The switching states, counter and time values of many SFs (see the "Special functions list -
SF (Page 156)" topic) can be set retentive. This means that current data values are retained
after a power failure, and that the block resumes operation at the break point. The timer is
not reset, but resumes operation until the time-to-go has expired, for example.
To enable this response, however, the relevant functions must be set retentive. Two options
are available:
R: The data is retained.
/: Current data is not retained (default). See the section in topic "Second circuit program
(Page 100)" on enabling and disabling retentivity.
The hours counter, weekly timer, yearly timer and PI controller are always retentive.
4.3.5 Parameter protection
In the parameter protection settings, you can determine whether or not the parameters can
be displayed and edited in LOGO! parameter assignment mode. Two options are available:
+: The parameter attribute permits read/write access in parameter assignment mode
(default).
-: The parameter settings are read–/write–protected in parameter assignment mode, and can
be edited only in programming mode. See the parameter protection mode example in the
Second circuit program (Page 100).
Note
Parameter protection covers only the "Set Param" window. If you embed variables of
protected special functions in a message text, the variables are still editable from the
message text. To protect these variables, you must also activate the protection of the
message text.